...I'd have to go reread the owners manual...but it probably has something to do with memory settings return to the last positions based on the key being used.
To work around (or with) someone else using your key and making changes to seat & mirror memory settings...you program them into the memory buttons on the seat...so that if someone else uses your car and changes things...the seats and mirrors remain in that settings because that same person may use the vehicle again and will require those positions (why should they have to readjust the seat again after just doing it prior to the first time they did it...especially if they just borrowed the vehicle to make a few runs before returning it to you?).
But when you get the car back and the settings have been changed...you can hit the memory button on the seat to recapture your original settings...then once you've driven the car and turn it off...the next time you get in...things will return to the settings of the last driver (you).
Check your owners manual to see if I'm at least close in my assumption.
